Catalytic etherification of phenols to alkyl aryl ethers

ABSTRACT

A process for etherifying phenols comprising reacting phenols at elevated temperature and pressure with a reactant selected from the group consisting of alcohol, ether and mixtures thereof in the presence of a catalyst comprising a sulfated oxide of a Group IIB metal selected from the group consisting of Zn, Cd, Hg and mixtures thereof on a support.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of this invention relates to the catalytic alkylation ofphenols to form alkyl aryl ethers.

2. The Prior Art

Heretofore it has been recognized that attendant with the development ofa synthetic fuels industry there will be an increase in the volume ofphenolic compounds which must be handled in processes for refiningand/or using synthetic crude. It is well known that phenolic compoundsare present in especially high concentrations when the source of thesynthetic crude is biomass or coal.

For example, phenolic compounds, such as phenol, cresol and theirhomologues, present in raw coal naphtha contribute to its instabilityand also tend to poison catalysts used to reform these naphthas toincrease their octane value. Before raw coal naphtha can be reformed toincrease its octane value, it must be hydrorefined or refined withhydrogen to eliminate sulfur and nitrogen compounds present thereinwhich would otherwise poison the reforming catalyst. If phenols arepresent in the raw naphtha during the hydrorefining operation, theoxygen present in the phenolic hydroxyl groups results in a hydrogendebit with no significant increase in the octane value of the naphtha.On the other hand, the corresponding alkyl aryl ethers of phenol orphenols, such as anisole, are useful blending agents for improving theoctane value of coal-derived naphthas. Therefore, it would beadvantageous to etherify the phenols derived from such naphthas.

Catalytic etherification of phenols with low molecular weight alkylalcohols, for example etherification of phenol with methanol to formanisole, was known heretofore. For example, U.S. Pat. No. 2,487,832 toSearle discloses that "solid dehydrating catalyst", such as activatedaluminas, and the oxides of thorium, tungsten, titanium, zirconium,molybdenum and chromium, can catalyze the etherification of phenol. U.S.Pat. No. 4,487,976 to Farcasio discloses that sulfated transition metaloxides, for example tungsten and hafnium, can catalyze theetherification of phenol and U.S. Pat. No. 4,450,306 to Eskinazidiscloses that La₂ (HPO₄), Sr(HSO₄)₂ and Ba(HSO₄)₂ can catalyze theetherification of phenols. While processes involving these catalysts mayhave merit, it would be desirable to have available other processesinvolving new catalysts which can present an opportunity to optimize thecatalytic etherification of phenol.

A problem with the etherification of phenols with alcohols is theconcurrent alkylation of the aromatic ring. Although the main product ofring methylation of phenol by methanol is ortho-cresol, the formation of2,6-xylenol can also occur. These ring methylated products have all theundesirable properties of phenol with respect to poisoning reformingcatalysts, etc. Therefore, a good etherification catalyst should notonly provide high conversion of phenols to ethers, but also should bemore selective to oxygen methylation than to ring methylation. Inaddition, a good etherification catalyst should be one that can beeasily formulated from readily available materials.

SUMMARY OF THE INVENTION

It has now been found that phenols can be etherified by contacting aphenolic feed with a reactant selected from the group consisting of analcohol, ether and mixtures thereof in the presence of a catalystcomprising a sulfated oxide of a Group IIB metal selected from the groupconsisting of Zn, Cd, Hg, and mixtures thereof on a support.

DETAILED DESCRIPTION OF THE INVENTION

Broadly stated, this invention is a process for etherifying phenolscomprising reacting phenols at elevated temperature and pressure with areactant selected from the group consisting of alcohol, ether andmixtures thereof in the presence of a catalyst comprising a sulfatedoxide of a Group IIB metal selected from the group consisting of Zn, Cd,Hg, and mixtures thereof on a suitable support. Preferably the catalystwill include an alkali promoter selected from the group comprising ofpotassium, lithium, sodium, and mixtures thereof.

The phenols employed in the process of the invention can include phenol,cresols, xylenols, naphthols and other substituted phenols, for example,substituted phenols found in coal liquids. The alcohols employed in theprocess of the invention can include any alcohol capable of etherifyingphenols. Generally C₁ to C₄ alcohols are preferred. Examples of suchpreferred alcohols are methanol, ethanol, propanol and mixtures thereof.Methanol is the most preferred reactant. A variety ethers can beemployed as a reactant in the process of the invention to etherifyphenols. Any ether capable of etherifying phenols can be employed as areactant. An example of a suitable ether is dimethylether. Suitableratios of phenols to reactants can be from about 0.1 to about 20 on aweight basis. Preferably an excess of reactant is employed.

In accordance with the process of this invention the phenols andetherifying reactants are contacted at elevated temperatures andpressures. Suitable temperatures can be from about 100° C. to about 600°C., preferably from about 200° C. to 500° C. Suitable pressures can befrom about 25 to about 1500 psig, preferably from about 50 to about 700psig.

The phenols and etherifying reactant in the presence of the catalyst ofthe invention are reacted for a time sufficient to etherify at least aportion of the phenols. In a stirred reactor, for example, suitableperiods of time can be from about 0.2 to about 100 seconds. In apreferred process mode gaseous phenols and reactant are passedcontinuously through a fixed bed reactor. In such a preferred process,gas hourly space velocities (GHSV) in the range of from about 10 toabout 10,000, preferably from about 100 to about 5,000, can be employed.The phenols/reactant gas hourly space velocity is a measure of thevolume of phenols and reactant at standard temperature and pressurepassing a given volume of catalyst in one hour.

Suitable supports include basic oxides, alumina, silica, carbon, orsuitable solid compounds of magnesium, calcium, strontium, and barium.The silicas include, for example, silica gel, diatomaceous earth, andcrystalline silicates. Preferably the support is porous and has arelatively high surface area. For example, very suitable supports canhave a surface area from about 20 to about 1,000 square meters per gramand a pore volume of from about 0.8 to 1.2 cc per gram. Especiallypreferred supports have a surface area in the range of from about 150 toabout 250 square meters per gram and a pore volume in the range of fromabout 0.8 to about 1.2 cc per grams. An example of a preferred supportis a relatively high surface area of alumina having a surface area andpore volume in the preferred range.

The catalyst composition employed in the process of the invention can beprepared by any of the well-known techniques such as impregnation,coprecipitation, incipient wetness and the like. If, for example, theincipient wetness technique is employed, a water soluble Group IIB metalsalt is dissolved in the minimum amount of water or an amount of watersufficient to fill the internal volume of the catalyst support at leastonce. This solution is then impregnated on the catalyst support followedby drying and reimpregnation until the total sample has been depositedon the support. Sufficient sulfuric acid is then impregnated on thecatalyst support to convert the Group IIB metal salt to its sulfateform. This material is then calcined in air, for example, at 1,000° F.for 4 hours. An alternative method involves the addition of the sulfuricacid to the solution of the Group IIB metal salt being used, and theimpregnation of this solution on the catalyst support. Anotheralternative method involves the impregnation of Group IIB metal sulfatesolution on to the catalyst support. Other well-known catalystpreparation techniques can be employed to prepare suitable catalystcompositions of the invention.

The Group IIB metal loadings can range from about 0.05 to 25 weightpercent metal based on the total weight of the catalyst, preferably fromabout 0.5 to about 10 weight percent and more preferably from about 1.5to about 5 weight percent. Preferably an amount of alkali promoter isincluded in the catalyst. The alkali promoter can be included in variousamounts and in a variety of ways. For example, a very suitable mannerfor including the alkali promoter is to impregnate a solution of alkalimetal hydroxide on the catalyst support used in the preparation of theGroup IIB metal catalyst composition of the invention.

As mentioned hereinbefore, the preferred support is a high surface areaalumina. This support including the Group IIB metal sulfate is thepreferred catalyst employed in the process of the invention. Thiscatalyst of the process of the invention is highly advantageous in thatit is formed from readily available Group IIB metals, for example,cadmium, and the catalyst provides excellent conversion and selectivitytowards etherification of phenols.

The following examples are provided to better illustrate the inventionby presenting several specific embodiments of the process of theinvention.

EXAMPLE I Part A (Catalyst Preparation)

A cadmium metal catalyst of this invention was prepared in the followingmanner:

Cadmium sulfate (1.28 gm) was dissolved in 20 cc 10% sulfuric acid. Thissolution was impregnated on alumina (25 gm; 20-40 mesh). The impregnatedalumina was dried at 110° C. in air and the impregnation was repeateduntil the total solution was deposited on the alumina support. Thecatalyst was then calcined under programmed conditions (4 hr at 200° F.,heating at increasing temperature at a rate of 200° F./hr for 4 hr, andholding for 4 hr at 1000° F. The catalyst was then vacuum sieved toremove any fines and used as such in the etherification process.

Part B (Etherification Process at Varying Temperatures)

The catalyst was loaded into a tubular reactor of approximately 0.37inch inside diameter. Enough catalyst was added (12.5 cc) to produce a15 cm bed. The bed was then heated to the various temperatures indicatedin Table I below. A solution of phenol in methanol (1 to 4 mole ratio)was passed over the catalyst bed at a rate of 1 cc/min. Pressure wasmaintained at 50 to 55 psig. The product from the reaction was collectedand analyzed by gas liquid chromatography. The percent conversionobtained as anisole and as all ethers (including anisole) at varioustemperatures is indicated in Table I below.

                  TABLE I    ______________________________________           Con-           version Anisole  Ethers Selectivey                                           Selectivity    Temp °C.           %       %        %      Anisole %                                           Ethers %    ______________________________________    275    8.8     8.8      8.8    100     100    285    21.8    21.8     21.8   100     100    295    27.8    27.2     27.5   97.6    98.8    300    35.3    34.0     34.9   96.4    99.0    305    41.1    39.1     40.5   95.2    98.6    310    41.7    39.1     40.9   93.8    98.2    315    50.8    46.1     49.5   90.9    97.5    320    54.8    48.0     52.9   87.6    96.5    325    58.6    46.4     53.8   79.0    91.7    330    57.8    41.7     50.1   72.2    86.7    ______________________________________

As can be seen from Table I, excellent conversion of phenols to ether isobtained when employing the preferred temperature ranges of theinvention. In cases set forth above selectivity to ethers is high.

Optimum temperatures to obtain optimum conversion and/or selectivity forparticular phenolic feeds and/or particular reactants can be determinedin a routine manner by employing procedures such as illustrated inExample II.

EXAMPLE II Part A (Catalyst Preparation)

A cadmium metal catalyst of this invention containing a promoter can beprepared in the following manner:

Potassium hydroxide (0.28 gm) is dissolved in water (20 gm). Thissolution is impregnated on alumina (25 gm; 20-40 mesh). The impregnatedalumina is dried at 110° C. in air and the impregnation is repeateduntil the total solution is deposited on the alumina support. Cadmiumsulfate (1.28 gm) is dissolved in sulfuric acid. The cadmium sulfatesolution is then deposited on the alumina support in a similar manner.The catalyst is then calcined under programmed conditions (4 hr at 200°F., heating at increased temperature at a rate of 200° F./hr for 4 hr,and holding for 4 hr at 1000° F. The potassium promoted cadmium metalcatalyst is then vacuum sieved to remove any fines and used as such inthe etherification process.

Part B (Etherification Process)

When the potassium promoted cadmium metal catalyst of Part A is employedin the etherification process set forth in Example II, Part B, goodresults are obtained in that there is excellent conversion of phenol tomethyl ethers and excellent selectivity to ethers.

What is claimed is:
 1. A process for etherifying phenols comprising reacting phenols at elevated temperature and pressure with a reactant selected from the group consisting of alcohol, ether and mixtures thereof in the presence of a catalyst comprising a sulfated oxide of a Group IIB metal selected from the group consisting of Zn, Cd, Hg and mixtures thereof on a support.
 2. The process of claim 1 wherein the catalyst includes a promoting amount of an alkali metal selected from the group consisting of potassium, lithium, sodium and mixtures thereof.
 3. The process of claim 1 wherein the Group IIB metal is cadmium.
 4. The process of claim 3 wherein the alkali metal is potassium.
 5. The process of claim 1 wherein the alcohol is selected from the group consisting of C₁ to C₄ alcohols.
 6. The process of claim 1 wherein the temperature is from about 100° C. to about 600° C.
 7. The process of claim 2 wherein the temperature is from about 200° C. to about 500° C.
 8. The process of claim 1 wherein the pressure is from about 25 to about 1500 psig.
 9. The process of claim 2 wherein the pressure is from about 50 to about 700 psig.
 10. The process of claim 3 wherein the alcohol is methanol.
 11. The process of claim 1 wherein the ether is dimethyl ether.
 12. The process of claim 1 wherein the support is a high surface area alumina. 